Quantum Supremacy: How the Quantum Computer Revolution Will Change Everything

by Michio Kaku

Turing and his colleagues set upon this crucial problem by designing calculating machines that might systematically crack these impenetrable codes. Their first breakthrough, called the bombe, resembled Babbage’s difference engine in some ways. Instead of steam-driven mechanisms like previous machines, whose gears and cogs were slow, difficult to make, and often jammed, the bombe relied on rotors, drums, and relays, all powered by electricity. But Turing was also involved with another project, Colossus, with an even more ingenious design. Historians believe it was the world’s first programmable digital electronic computer. Instead of mechanical parts like the difference engine or the bombe, they used vacuum tubes, which can send electrical signals near the speed of light. Vacuum tubes can be compared to valves controlling the flow of water. By turning a small valve, one can shut off the water flowing in a much larger pipe, or let it flow unimpeded. This, in turn, can represent the number 0 or 1. So a system of water pipes and valves can represent a digital computer, where the water is like the flow of electricity. In the machines at Bletchley Park, a large array of vacuum tubes could perform digital calculations at enormous speeds by turning the flow of electricity on or off in the vacuum tubes. Thus, the work of Turing and others replaced the analog computer with a digital computer. One version of Colossus contained 2,400 vacuum tubes and filled up an entire room.